Cylinder of internal combustion engines



April 13, 1937. HIR. RICARDO CYLINDER 0F INTERNAL COMBUSTION ENGINES Filed Sept. 17, 1928 Y 2 Sheets-Sheet 1 0-5 0&4.

April 13, 1937. H. R. RICARDO 2,076,593

I I CYLINDER OF INTERNAL COMBUSTION ENGINES I Filed sap-t. 17, 1928 2 Sheets-Sheet 2 Patented Apr. 13, 1937 PATENT OFFICE CYLINDER OF INTERNAL COMBUSTION ENGINES Harry Ralph Ricardo, London, England Application September 17,1928, Serial No. 306,526

In Great Britain October 5, 1927 l 16 Claims.

The present invention relates to cylinders of internal combustion engines and more particularly to the formation of the combustion space in poppet valve internal combustion engines of 5 the class which operate upon the constant volume cycle wherein the air and fuel are mixed intimately previous to compression and the combustion process. The invention relates to that type of engine of the above class known as side-valve 1O engines in which the valves are located at the side of the engine cylinder as distinguished from overhead valve engines.

The object of the present invention is to provide an improved form of combustion chamber for engines of the type indicated which, while promoting a high thermal efficiency and a reduced tendency to detonation, will result in a smooth running engine free from roughness.

Further objects and features ,of the invention 2 will be apparent from the following description thereof taken in connection with the accompanying drawings, in which I Figure l is a graphical representation of the eifect on the performance of an internal combus- 25 tion engine obtained by altering the form of the combustion space, consisting of two superimposed crank angle base indicator diagrams;

Figure 2 represents the effect of turbulence of an internal combustion engine fuel charge on the 39 tendency to detonate the charge;

Figures 3 and 4 are graphical representations illustrating the effect of turbulence on the efiiciency of the engine;

Figure 5 is a sectional plan through one form of combustion chamber embodying the principles of the present invention and taken on the line 5-5 of Figure 7;

Figure 6 is a section on the line 6-6 of 40 Figure 5,

Figure 5;

Figure 8 is a graphical representation similar to Figure 1; and Figure 9 is a partial sectional view corresponding to Figure 5 but illustrating a slightly modified form of combustion chamber.

In all practicable reciprocating internal combustion engines it is essential that some degree of 5 turbulence of the charge or a part of the charge shall exist at the moment ofignition. It is well known from experiments made in closed vessels on stagnant explosive mixtures that the maximum rate of inflammation attainable by 5 simple ignition of the stagnant charge issolow Figure '7 is a section on the line 1--| of that it would be impossible to run engines at even one hundred revolutions per minute if the cylinder contents were truly stagnant.

Turbulence is essential in order:--- I (1) To spread combustion rapidly throughout the whole mass of the working fluid.

(2) To scour away from the surfaces the thin layer of gas which normally adheres so closely to the coolwalls as either completely to escape combustion or to burn so late in the expansion 10 stroke as to be of little value.

(3) To check detonation (a) by keeping the as-yet unburned portion of gas in rapid motion so that it may the more readily get rid to the containing walls of the heat produced by compression from the advancing flame front and (b) by preventing the isolation of pockets of relatively stagnant unburned gas in positions where they can be compressed and detonated by the advancing flame front.

In practice all reciprocating internal combustion engines take in their fresh charges of air or air and combustible through valves or'ports at I an appreciable velocity. This velocity of entry causes a degree of turbulence of the charge within the cylinder and combustion space which accelerates the rate of inflammation sufiiciently to enable such engines to run at relatively high speeds.

It may be desirable to define what is meant by the expression turbulence of the charge. By turbulence is meant a state'of motion' of the gases forming the combustible charge as opposed to a stagnant state in which motion is either entirely absent or is of such a small order that inflammation can spread by contact from particle to particle at a rate substantially as great as that at which the particles are moving'. Turbulencemay exist in several forms of which the principal forms appear to be as follows: p 40 (1) General .turbulence in which particles are moving in all directions. i

(2) Organized turbulence in which substantially the whole body of the charge is involved in a unidirectional state of motion. (3) Eddying turbulence in which a portion or several portions of the charge are in a state of independent unidirectional motion.

It has been found that the performance of any internal combustion engine operating on the constant volume cycle depends primarily upon both the extent and the nature of the turbulence of the charge at the time of inflammation.

Turbulence of the major portion of the charge 55 may exist from, any one of the following causes or from a combination of any or all of them:-

a. The high enteringyelocity ot the gases through the inlet orifice.

5 b. Mechanical disturbance of the charge within the combustion space produced during the compression stroke by forcing the charge from the cylinder into the combustion space through a port or other restricted part or passage as, for,

example, by the means described and claimed in the specification. of the-present inventors Letters General turbulence .and eddying turbulence may be produced in a side-valveenglne by any of the causes enumerated above. It is diflicult, however, in a normal side-valve engine to produce true organized turbulence although in an overhead or in a sleeve valve engine, a very high de-,

gree of such turbulence may readily be produced I if desired.

' It has been' found that in a homogeneous charge engine true organized turbulence is an undesirable feature owing to the fact that, when '35 the ignition spark passes, the nucleus of flame created in the body of the charge is carried round at the same rate as the rotating body of gas so that spread of inflammation depends almost entirely upon contact of inflamed particle toun- 40 inflamed particle, resulting in a slow spread of the flame as distinct from the rapid general dissemination of inflammation which occurs when general turbulence exists.v

Experiment has shown also that of the three forms of turbulence, the form described as "general is of the greatest practical use for engines operating on the constant volume cycle for the reason that it promotes most favourablycomplete and rapid spread of inflammation,

scouring of the walls, and suppression of'detonation. As regards the last feature, experiment has shown that, so long'as the turbulence is general, the tendency to detonate decreasesin inverse ratio to the degree of turbulence.

Further it has been observed that detonation occurs only inthat portion of the working fluid most remote from the point of ignition and that in order to reduce further the tendency to detonate it is essential that:

' (1) The distance from the point of ignition to G0 the farthest point in the combustion chamber shall be kept as short as possible, and

(2) The part of the working fluid which is most remote from the source of ignition shall be in 5 state of high general turbulence both in order to disseminate the flame uniformly throughout its bulk and at the same time in order that it may the more readily get rid to the containing walls of the heat of compression caused by the 70 advancing flame front.

As the degree of general turbulence existing in a side-valve engine is, for equal conditions as to'mixture strength and compression ratio, the

factor. controlling the rate of pressure rise, it is 75 possible by means of indicator diagrams to ascertain the degree of turbulencepresent by-measuring the rate of pressure rise during combustion. This rate may conveniently be expressed as pounds ,per square inch pressure rise per degree of crank angle.

By wayv of.illustrating the effectof general" turbulence on pressure rise, there is shown in Figure 1 of the accompanying drawings, two superimposed crank angle base indicator diagrams both taken fromthe same side-valve engine under identical conditions of compression ratio, mixture strength and speed of rdtation. The cylinder head of the engine being detachable it is possible to change readily the form of the combustion space. The curve A shows the pressurerise on ignition which occurred when a head designed to give low general turbulence was in use, while curve B shows the pressure rise when employing a head giving a high degree of general" turbulence.

It will be seen that in the case of curve A the slope of the explosion line, i. e. the rate of pressure rise per degree of crank angle is 23 pounds per square inch while in curve B the rate is pounds per square inch. It was observed when making this experiment that when operating with the head giving diagram A the running of the engine was extremely soft and quiet, while with the head giving diagram B'the running was harsh, rough and noisy.

A series of experiments on heads having various degrees of turbulence, but all giving the same compression ratio, proved that the tendency to detonate was markedly reduced as the degree of general turbulence was increased. In order to obtain a measure of this tendency, the following test was made at each stage of turbulenc e:'Iwo fuels, one having a high resistance to detonation and the other a low resistance, were taken and blended to give a fuel which, when used with the particular head being tested, would just detonate under given conditions of load and mixture strength. The curve set out in Figure 2 of the accompanying drawings-shows the results obtained. In this figure the ordinates give resistance' to detonation in terms of equivalent compression ratio while the abscissae show pressure rise in pounds per squareinchper degree of crank angle. From this figure it will be seen that as the rate of pressure rise is increased from 23 pounds per square inch to 'pounds per square inch per degree of crank angle, the tendency to detonate is reduced. That is to say, given a fuel which just detonates' at a compression ratio of 5.2:1 when the general turbulence is such as to give a pressure rise of 23 pounds per square inch, then if the general turbulence is increased so as to give a pressure rise of 65 poun ds per square inch per degree of crank angle, the compression ratio can be raised to 72:1 at which ratio the same fuel will again just detonate.

It has been found by experiment that, the highest efliciency is obtained in an engine of normal side-valve design when.the rate of pressure rise denoting the degree of general turbulence is of the order of 30-35 pounds per square'inch When the rate of.

per degree of crank angle. pressure rise greatly exceeds 30 pounds per square inch per degree of crank angle, the loss of heat due to the violent scrubbing of the 'hot gases gagainstthe walls of the combustion chamber, -becomes such as to outweigh the advantage per degree of crank angle, the eficiency falls owing to delayed and incomplete combustion.

This is well illustrated bythe curve in Figure 3 of the accompanying drawings in which the ordi- 5 nates show the minimum fuel consumption on full throttle expressed in pints per indicated horse-power hour plotted on a base of pressure rise in pounds per square inch per degree of crank angle. Figure 4 of the accompanying 0 drawings shows a similar curve under part load conditions, the engine being throttled in each case to give an indicated mean effective pressure of 55 pounds per square inch.

It would appear that the optimum rate of pressure rise lies between the limits of 25 to 40 pounds per square inch per degree of crank angle depending to some extent upon the size and general design of the engine, the stifi'er the design the higher the rate permissible without developing roughness.

It has been found, however, that when the whole of the gas is in a state of high general turbulence, the resulting rapid pressure rise causes spring of such parts as the connecting rod, crankshaft, etc., and therefore gives rise to an indeterminate drumming-noise accompanied by a high periodicity vibrationa condition generally known as rough running.

Further investigation has shown that if the pressure he applied slowly at first with a view to taking up the spring of the aforesaid parts, it may be applied subsequently at a very high rate indeed without any trace of roughness or drumming.

According to this invention the combustion chamber of an engine of the above type operating with a homogeneous charge is so formed that the portion of the working fluid which is first ignited burns at a relatively slow rate of pressure rise while the remaining part burns at a relatively high rate of pressure rise, thefgeneral turbulence of the main part of the charge being augmented by the expansion of the small first ignited portion. Thus-the combustion chamber is conveniently so formed and the ignition device so situated therein that the ignition is initiated in a small part of the charge which is in a relatively non-turbulent state as compared with the state of the main part of the charge so that the first ignited part of the charge burns at a relatively slow rate of pressure rise until the flame spreads to the main part of the charge after which the rate of pressure rise is rapid, the general turbulence of the main part of the charge being augmented by the expansion of the first ignited relatively non-turbulent part thereof.

In a convenient construction according to this invention the combustion chamber of an engine of the type indicated which does not form part 0 of the cylinder bore but overlaps the latter and is in open communication therewith, comprises a main part and a subsidiary part whose volume is appreciably less than that of the main part, this subsidiary part of the combustion chamber 5 being constructed and arranged so that while it is open to and in free communication with the rest of the combustion chamber there will lie in this subsidiary part towards the end of the compression stroke a portion of the charge constituting not more and preferably less than 25% of the whole charge, this lesser part of the charge being then in a stagnant or non-turbulent state compared to the state of the main portion of the charge, the lesser part of the charge being ignited r5 first when it will inflame less rapidly than the main' portion of the charge will burn when the flame spreads thereto, the expansion of the lesser portion of the charge after ignition causing turbulence of a general type in the main portion of the charge. The mainpart of the combustion chamber, that is to say the part of larger volume, has a compact form and when measured in the direction of the cylinder axis is deep in relation to the other part of the combustion chamber which is shallower and of less volume than that of the main part. This smaller part constitutes a pocket or recess whose construction, position and dimensions are such that while it isin free and unrestricted communication with themain part of the combustion chamber the desired 25% or less of the whole charge will lie in this pocket towards the end of the compression stroke, this lesser portion of the charge being then in a comparatively stagnant or non-turbulent state so that when ignited first by means situated in the shallow pocket it must burn less rapidly than the main portion of the charge when the flame spreads thereto. As an instance of the improved structure the combustion chamber is so formed as to overlap the cylinder bore and also extend laterally where it lies over or contains the valves. In this lateral part of the combustion chamber is a projection or indentation which reduces substantially the depth or measurement in the direction of the cylinder axis of a portion of the chamber and forms a shallow pocket or recess in which is situated the means for igniting the charge.

' The said projecting part has a shape which produces abrupt changes in the dimensions of that part of the chamber where the shallow pocket opens in a free and unrestricted manner into the main part of the chamber. Thus the main and larger part of the combustion chamber has a compact general formation while a part of the wall of the combustion chamber extends inwards in a manner such that sections taken through the chamber and this part of the wall show'abrupt changes -in the dimensions of the two adjacent parts of the chamber, theinwardly projecting portion of the wall forming beneath it the shallowpocket or recess whose construction, position and dimensions while giving free and unrestricted communication with and opening abruptly into the main part of the combustion chamber ensures the retention in the. pocket at the end of the compression stroke of 25% or less of the whole charge in a relativelystagnant or nonturbulent state.

A combustion chamber embodying the present invention as indicated above eliminates roughness by enabling a small portion of the charge,

'of the order of 10% to 20%, to burn at a relatively slow rate of pressure rise in order to take up the spring referred to above and it promotes a high thermal efficiency and a reduced tendency to detonate by burning the main portion of the charge at a rate lying between the limits of 20 to 40 pounds per square inch per degree of crank angle.

The main part of the combustion chamber,

' that is to say, the portion distinct from the shallow pocket or recess, is made as deep, measured in the direction of the cylinder axis, and

r as compact, with respect to its dimensions in directions normal to the cylinder axis, as circumstances such as the position of the valves will permit. In the improved structure no special means are provided to promote turbulence either during the suction stroke or during the compression stroke in the manner indicated under heading b above, and as claimed in the specification of the present inventors prior Letters Patent of the United States of America No. 1,474,003. It must be observed, however, that, owing to the general form of the cylinder head being similar to that disclosed in the earlier specification referred to, some general turbulence of the charge will inevitably be produced during its passage on the compression stroke from the cylinder bore into the combustion spaces. However, as explained later in the present specification, the reason that thisparticular form of cylinder head is employed in the present instance is in order to displace combustion chamber volume lying over a considerable portion of the piston area, for

the purpose of providing a deep main combustion space and of reducing the length of flame travel. In the present construction the requisite degree and type or form of turbulence is produced in the main part of the combustion chamber primarily by the ignition and subsequent expansion of the gases contained in the shallow pocket. The general turbulence thus obtained may however be aided by disturbance broughtabout mechanically by arranging for the near approach of the piston or some portion thereof to some part of the cylinder head, such an arrangement in itself being a known method of producing mechanical disturbance as indicated under the head ing 0 above when referring to various methods of producing turbulence. Thus in order to ensure that the turbulence shall be of the type indicated' above as general, it is desirable to avoid any formation in the nature of a constriction between the shallow pocket and the main part of the combustion chamber, but on the other hand the shallow pocket shall be in free and unrestricted communication with the main part of thecombustion chamber while the 40 shallow pocket shall also open in an abrupt manner into the main part of the combustion chamber in order that the sudden change of section between the parts of the combustion chamber shall break up and distribute more uniformly the advancing fiame front. The shallow pocket may be placed over the inlet valve, over the exhaust valve or over both valves, or situated in some other convenient position. The capacity of this pocket should represent preferably from about 10% to 20% of that of the entire combustion space.

The invention maybe carried into practice in various ways but one construction according to this invention is illustrated by way of example in Figures 5, 6 and 7 of the accompanying drawings.

In the construction illustrated in Figures 5, 6 and '7, the engine comprises a cylinder block E 'in which are formed cylinder bores iii and inlet and exhaust passages E, E controlled respectively by valves F H Carried by the cylinder block E is a cylinder head member C in which are formed the combustion chambers.

, The cylinder head and cylinder block are so formed as shown that each combustion chamber comprises a main part C with a smaller part D constituting a shallow pocket or recess which opens into the main part C". The main part C of each combustion chamber overlaps its associated cylinder bore E and also lies over one of the valves (the inlet valve F in the construction illustrated) as shown. A part G of the upper wall of the combustion'chamber is carried inwards to form a projection which extends over the valve H thereby forming the shallow pocket D over this valve. This inwardly projecting part G has a screwthreaded bore G formed therein to receive a sparking plug and is so shaped that sections taken through the main part of the combustion chamber and this projection show, as between the main part C of the combustion chamber and the pocket D abrupt changes in the dimensions of'the combustion chamber measured in thedirection of the cylinder axis as indicated in Figures 6 and '7. In order to make the pocket D of the desired small depth measured in a direction parallel to the cylinder axis, it may in some cases be necessary to provide for the mechanical clearance of the valve or valves which lie in the pocket by recessing slightly the underside of the projection G as indicated at G. This recessing can conveniently be eflected in the case of one valve by chamfering the mouth v of the bore in which the sparking plug lies and if/the pocket lies over both valves, by providing an indentation in the wall of v the pocket over the other valve.

The remaining part J of the cylinder head I Whichles over each cylinder bore E is given the same formation, that is'to say, either fiat or otherwise, as the face of the piston K so that at the end of the compressionstroke these parts may approach each other as closely as is practicable having regard to mechanical conditions as indicated in '7.

It should be noted that the combustion of the amount of this capacity is determined from considerations regarding the stifiness of the engine structure as a whole, the capacity of this space approaching nearer to the upper limit specified the weaker the structure in order more eflectually to take up the spring" of the parts. From-the point of view of eliminating detonation it is clesirable that the distance from the line of emergence of the fiame from the shallow pocket to the boundary walls of the combustion chamber, as, indicated for example by the arrow-headed lines L in Figure 5, shall be kept as short as possible a condition which, in a side-valve engine, favours placing the shallow pocket over one or both of the valves rather than on the side of the combustion chamber remote from the valves. Figure 9 illustrates an arrangement in which the pocket lies over both of the valves. Thus in this figure the line G indicates the approximate configurationof the depending shelf, 6 indicates the spark plug opening, while the inlet and exhaust valves are respectively indicated at F and H It has been found by experiment that a very thin film of working fluid such as may'be en-' trapped between the piston and head when these two members are brought into close proximity as indicated in Figure 7, is able when ignition is initiated in the main portion ofthe chargeto get rid of its heat so rapidly to the containing walls that it cannot be raised bycompression due tothe advancing flame front to such a temperature as will cause detonation. By such means it is possible to displace combustion chamber volume lying over a considerable portion of the piston area. To accomplish this it is not necessary that the piston or cylinder head shall be flat as shown, so long as one surface conforms approximately to the other. By such means therefore the length of flame travel from the line of emergence of the flame from the shallow chamber to the farthest point in the deep portion of the combustion chamber may be reduced to a considerable extent when the shallow pocket is situated over the valves, see Figure 7.

With regard'to the thin layer of gas referred to, it has been found that provided the thickness of the layer does not exceed 0.16 inch, there is no liability to detonation of the gas entrapped between the piston and head when the point of ignition is located anywhere in the main body of the charge. If, however, the dimension named is exceeded, the tendency to detonate increases rapidly with increase in the thickness of the layer. The increase in tendency to detonate is such that given a fuel which just detonates with a compression ratio of 5 1 with a layer 0.209 inch thick, an increase in thickness to 0.271 inch necessitates reduction of the compression ratio to 4.75: 1 to give the same degree of detonation when using the same fuel, while there isno liability to detonate the thin layer of gas provided its depth does not exceed 0.16 inch.

It will be observed that by causing the piston top to approach closely the cylinder head some mechanical disturbance of the main charge will be produced. This source of general turbulence however, is a secondary consideration only and the close approach of the parts in question is adopted primarily to enable a deep main combustion space of the desired form to be provided.

In order to illustrate the functional diiference between a combustion space embodying the present invention for example as shown in Figures 5, 6 and 7, and a combustion space not embodying the present invention, there are shown in Figure 8 of the accompanying drawings two superimposed indicator diagrams. These diagrams were taken using first one head and then the other on the same engine. The compression ratio, mixture strength and engine speed were the same in both cases. The rate of pressure rise per degree of crank angle is substantially the same in both cases, namely, 36 pounds per square inch per degree of crank angle thus indicating that the same order of general turbulence of the main charge existed in both cases. The essential point of difierence between the two diagrams lies in the nature of the transition curves M and N which join the compression curve 0 with the rapidly rising pressure lines P and Q representing the combustion periods. The curve 0MP represents the diagram obtained from the earlier form of head, and the curve O NQ that given by a head embodying the present invention. It will be observed that in the case of the diagram 0MP the transition curve M is a reversed curve which at first tends to follow the non-firing compression curve 00 In the case of diagram ONQ the I transition curve N flows uniformly and smoothly from the compression curve 0 into the pressure rise curve Q. It has been found that it is this gradual merging of the compression line into the explosion line which is caused by the relatively slow burning of the 10% to 20% portion of the charge, which enables the spring of structural parts to be taken up without roughness. The running of the engine with the head giving curve ONQ was smooth, while with the head giving curve 0MP, the running was rough, although in both cases the mixture strength employed was that giving maximum power.

As has been stated already, a combustion space embodying the present invention achieves its object by burning a small portion of the charge at a relatively slow rate and the main portion of the charge at a relatively high rate, and limits for the rate at which the main portion may be burnt have been indicated. It is, however, impracticable to specify the slower rate at which the smaller portion shall be burnt. It may be pointed out, however, that the sources of general turbulence of this small portion of the charge are the sources already referred to under the headings a and 0 above, and that its turbulence is subject to damping by the proximity of the walls of the pocket or recess. If the damping is somewhat too great then an earlier timing of the ignition will be required, while if the damping is insufficient then the transition curve N may be too abrupt to give smooth running, in which case more damping may be given by'extending the area of the recess and in some cases by reducing its depth measured in the direction of the cylinder axis.

It will be understood from the foregoing description that in a combustion space embodying the present invention the main portion of the charge is immediately prior to ignition in a state of general turbulence due to the causes a and 0 previously mentioned and that immediately after the inflammation of the small portion contained in the pocket, the main charge has additional general turbulence imparted to it from cause d. I

What I claim as my invention and desire to secure by Letters Patent is:-

1. In an internal combustion engine the combination of a cylinder with valve-controlled inlet and exhaust ports situated at the side thereof, a combustion chamber at the end of the cylinder lying over the valve-controlled ports with a part of it overlapping a portion of the cylinder bore with which the combustion chamber is in open communication, an inwardly directed projection in the combustion chamber forming beneath it and in the neighbourhood of bustion chamber a portion of the charge constituting not more than 25% of the whole gase-' ous charge, and means for igniting first that part of the charge which lies in the said subsidi-ary part of the combustion chamber.

2. In an internal combustion engine the combination of .a cylinder with valve-controlled inlet and exhaust ports situated at the side thereof, a combustion chamber at the end of the cylinder lying over the valve-controlled ports with a part of it overlapping a portion of the cylinder bor'e with which the combustion chamber is in open communication, a recess in the combustion chamber which is open to and in free communication with the main part of the combustion chamber this recess being formed by indenting the wall of the combustion chamber in the neighbourhood of one of said valves and thereby reducing materially the depth measurement of that part of the combustion chamber in the direction of the cylinder axis, the volume of this recess being such that at the end of the compression stroke there will lie in it a portion of the charge constituting not more than 25% of the whole gaseous charge, and means for igniting first that part of the charge which lies in the said recess in the combustion chamber.

3. In an internal combustion engine the combination of a cylinder with valve-controlled inlet and exhaust ports situated at the side thereof, acombustion chamber at the end of the cyl- 10 inder lying over the valve-controlled ports with a part of it overlapping a portion of the cylinder bore with which the combustion chamber is in open communication, a recess in the combustion chamber which is open to and in free communication with the main part of the combustion chamber this recess being formed by indenting the wall of the combustion chamber in the neighbourhood of one of said valves and thereby reducing materially the depth measurement of that part of the combustion chamber in the direction of the cylinder axis, the formation of the combustion chamber wall at the edge of the indentation being such that the change in the depth measurement of the combustion chamber takes place abruptly, the volume of this recess being such that at the end of the compression stroke there will lie in it a portion of the charge constituting not more than 25% of the whole gaseous 7 charge, and means for igniting first that part of the charge which lies in the said recess in the combustion chamber.

7 4. An internal combustion engine including in combination a cylinder with valve-controlled inlet and exhaust ports at theside thereof, a cylinder head so formed that between it and the cylinder is provided a combustion chamber lying over the valve-controlled ports and overlapping a portion of the cylinder bore with which the combustion chamber is thus in open communication, a part of this combustion chamber which at the end of the compression stroke contains not more than 25% of the whole gaseous charge and is open to and in free communication with the remaining part of the chamber having small dimansions measured in a direction parallel to the cylinder axis as compared with the main part of the combustion chamber, and means for igniting first the part of the charge which lies in the said subsidiary part of the combustion chamber.

5. An internal combustion engine including in combination a cylinder with valve-controlled inlet and exhaustvports situated at the side thereof, a combustion chamber at the end of the cylinder lying over the valve-controlled ports with a part of it overlapping a portion of the cylinder bore with which the combustion chamber is thus in open communication, an inwardly directed projection in the combustion chamber forming beneath it and in the neighborhood'of at least one v of the ports a subsidiary pocket-like part of the combination 'a cylinder with valve-controlled in let and exhaust ports at the side thereof, a piston within said cylinder, a cylinder head overlying said ports and said cylinder to provide a combus- 6. An internal combustion engine including in tion chamber, said cylinder head conforming closely to a portion, remote from said ports, of

the upper surface of the piston in its uppermost position, and being depressed in the vicinity of said ports to form a subsidiary pocket and ignition means in said pocket.

7. In an internal combustion engine, the combination with a cylinder block having a cylinder formed therein and having inlet andexhaust ports, of a piston operable in said cylinder, a cylinder head forming with said cylinder block a compression chamber communicating with said ports and said cylinder, said chamber having a varying depth measured axially. of the cylinder, being or minimum depth aiiording mechanical piston clearance only over a portion of the cylinder area, of considerable depth over the remainder of the cylinder area, and having portions of maximum depth and substantially less than maximum depth over a portion of said cylinder block laterally of the cylinder, that portion of the compression chamber of substantially less than maximum depth aflording a subsidiary pocket, and ignition means in said pocket.

8. In an internal combustion engine, the combination with a cylinder block having a cylinder formed therein and having inlet and exhaust ports, of a piston operable in said cylinder, a cylinder head forming with said cylinder block a compression chamber communicating with said ports and said cylinder, said chamber having a varyingdepth measured axially of the cylinder, being of minimum depth ail'ording mechanical piston clearance only over a portion of the cylinder area, of considerable depth over the remainder of the cylinder area, and having portions of maximum depth and substantially less than maximum depth over a portion of said cylinder block laterally of the cylinder, that portion of the compression chamber of substantially less than maximum depth affording a subsidiary pocket, the volume of said subsidiary pocket constituting a minor part only of the entire volume of the combustion chamber, and ignition means in said pocket. p 9. In an internal combustion engine, the combination with a cylinder block having a cylinder formed therein and having inlet and exhaust .ports disposed laterally of saidcylinder, of a municating with said ports and said cylinder, said chamber having a varying depth measured axially of the cylinder, being of minimum depth ai'l'ording mechanical piston clearance only over a portion of the cylinder area, of considerable depth over the remainder of the cylinder area, and having portions of maximum depth and substantially less than maximum depth over a portion of said cylinder block laterally of the cylinder, that portion of the compression chamber of substantially less than maximum depth extending over at least one of said ports and aifording a subsidiary pocket,

:and ignition means in said pocket.

10. In an L-head internal combustion engine, a block including a cylinder, a piston reciprocating in the cylinder, inlet and exhaust passages in the block, valves controlling said passages. a head seating upon the block and having a compression chamber overlying said valves and the cylinder area and being of minimum depth commensurate with adequate clearance for the piston over a portion only of the cylinder area, the roof of the chamber having adepending shelf above the exhaust valve and forming therewith and with the adjacent portion of the block a shielded space, and means for igniting the charge in said space.

11. In an L-head internal combustion engine, a block including a cylinder, a piston reciprocating in the cylinder, inlet and exhaust passages in the block, Valves controllin said passages, a head seating upon the block and having a compression chamber overlying the valves and the cylinder area and being of minimum depth com.- mensurate with adequate clearance for the piston over a portion only of the cylinder area, the roof of the chamber having-a depending shelf above the valves and the intermediate portion of the block and forming therewith a shielded space, and means for igniting the charge in said space.

12. In an L-head internal combustion engine, a block including a cylinder, a piston reciprocating in the cylinder, inlet and exhaust passages in the block, valves controlling said passages, a head seating upon the block-and having a compression chamber overlying the valves and the cylinder area and being of minimum depth commensurate with adequate clearance for the piston over a portion only of the cylinder area, the roof of the chamber having a depending shelf above a portion of the block and forming therewith a shielded space, and means for igniting the area, the head lying in close proximity to the piston in its uppermost position over a portion only ofthe cylinder area, the roof of the chamher being depressed over the exhaust valve to form a pocket affording a minor portion of the total volume of the chamber, and means for igniting the charge in said pocket.

14. In an internal combustion engine of the L-head type, a compression chamber of substantial triangular cross-section and having itsvolume distributed between three portions of different depth, inlet and exhaust valves opening into said chamber, one of said valves being in one corner of the triangle adjacent the portion of greatest depth, the other of said valves being at another corner of the triangle, and that portion being of intermediate depth, and the top of the engine piston being at the third corner of the triangle and adjacent the portion of least depth, and ignition means disposed in that portion'of intermediate depth.

15. An internal combustion engine including in combination a cylinder with poppet valve controlled inlet and exhaust ports at the side thereof, a cylinder head providing a compression chamber overlying said ports and a portion of said cylinder, said compression chamber being of materially less depth adjacent said exhaust port than adjacent said inlet port, the depth of said chamber adjacent said exhaust port being not materially greater than that required to afiord clearance for the exhaust valve in the opened position of the latter, and ignition means disposed in that portion of substantiallyless depth.

16. In an internal combustion engine of the L-head type, a compression chamber having inlet and exhaust'valves'opening into the said chamher, said chamber having a portion of greater depth adjacent one of said valves and a portion of substantially less depth adjacent the other of said valves, said portions of the chamber being in direct communication, said chamber having a third portion of less depth than either of the portions adjacent the valves, said third portion being directly adjacent the piston of the engine when it is at the top of its stroke, and ignition means disposed in that portion of less depth which is adjacent one of the valves.

HARRY RALPH RICARDO. 

